What is Tysabri's role in treating MS and what are the side effects of treatment? Irish TimesMedical Correspondent Dr Muiris Houstonexplains.
What is MS?
Multiple sclerosis (MS) is a chronic neurological disorder. It attacks the brain and spinal cord by destroying the sheaths that cover nerve fibres and damages the nerve fibres themselves.
The term multiple sclerosis refers to the many areas of scarring (sclerosis) that results from the loss of nerve sheaths. The scarring interferes with the smooth transmission of impulses travelling along the nerve to and from the brain.
How common is the disease?
MS affects about 7,000 people in the Republic. In the northwest, the prevalence of the disease can be as high as 1 in 400. It usually begins between the ages of 20 and 40 and is more common in women.
Most people with the disease have periods of relatively good health (remissions) alternating with debilitating flare-ups (relapses).
What causes MS?
It is not known what causes MS, but it is thought that a virus or other outside agent somehow triggers the immune system into attacking itself. MS is not hereditary, but having a family member with the condition increases the risk of developing it.
What are the symptoms?
The symptoms of MS are highly variable and individualised, but include mood symptoms, tremor and difficulty maintaining balance. Double vision, numbness/tingling and heat sensitivity are also common. Profound fatigue is a disabling feature of the disease.
Can it be treated?
There is no cure for MS. Treatment options include the short-term use of steroids and interferon injections which are used to limit progression of the disease. Tysabri is the newest form of disease modifying treatment.
What are the side effects of Tysabri?
Tysabri works by dampening down the immune system. However, this has the unwanted side effect of making the patient more vulnerable to infections such as pneumonia and tuberculosis. Progressive multifocal leukoencephalopathy (PML) is a rare side effect caused by the activation of the JC virus, which 80 per cent of people carry in a latent form in the body.
PML progressively damages the central nervous system.
So should the drug have been licensed?
All drugs are assessed on a risk benefit ratio. Treatment for minor conditions would not receive a licence once serious side effects such as PML were identified.
But for more serious diseases, such as MS and cancer, drug regulators calculate that informed patients should have the option to balance the risk of a side effect against the life-enabling properties of a ground-breaking medication.
What should patients on Tysabri do at this point?
There is no need to stop taking Tysabri following yesterday's news. The drug remains on the market as the discovery of two new cases of PML shows the surveillance put in place by drug regulators actually works.
However, patients should check at their next routine appointment with their nurse specialist or consultant that they are being fully monitored at appropriate intervals.
They could also ask those looking after their treatment whether they are experiencing any difficulty looking after them because of HSE cutbacks or budget shortfalls.
For more information contact the MS Ireland helpline: 1850 233 233